1. Field of the Invention
The present invention relates a method and apparatus for obtaining an injection pressure curve as a molding condition, and a recording medium on which the method is recorded. More particularly, the present invention relates to a method and apparatus for obtaining an injection pressure curve serving as a molding condition by using an injection pressure curve obtained by a resin flow analysis, and a computer readable storage medium which stores a program for causing a computer to execute the method.
2. Description of the Prior Art
There is known an injection pressure control system in which, in molding in an injection molding machine, a predetermined injection pressure curve in the injection (filling) step is set as one of molding conditions, and the injection pressure is controlled in the injection step so that the set injection pressure curve is equal to an actual injection pressure curve.
As a method of obtaining resin pressure at any position in a die by performing a flow analysis of resin in the die, resin flow analysis CAE (Computer Aided Engineering) is developed (see xe2x80x9cResin flow analysis CAE systemxe2x80x9d on pages 210 to 214 of the tenth revised edition of xe2x80x9cInjection moldingxe2x80x9d edited by Itochu Corp. and two other persons and issued by Plastic Age Inc. on Aug. 10, 1993). In this resin flow analysis CAE, die temperature, flow rate of melted resin in a resin inlet port (nozzle end viewed from the injection molding machine side) in the die, and resin temperature are given as analysis conditions, and a flow analysis in the die is performed, so that pressure variations based on the resin inlet port are calculated.
Although a method of directly giving the analysis conditions to be given to the resin flow analysis CAE to a molding machine to perform molding is employed, since the mechanical characteristics of the injection molding machine and the compression behavior in the cylinder or nozzle of the injection molding machine are not reflected on the molding conditions, the results of the resin flow analysis cannot be directly used as mass production conditions.
In general in the injection molding machine, a pressure sensor for detecting pressure variations is attached to the rear end portion of a screw, and a nozzle portion, a cylinder portion, and the like are arranged between the resin inlet port of the die and the pressure sensor. Since the nozzle end portion (portion coming into contact with the die) is sharply constricted in many cases, though the pressure is detected by the pressure sensor immediately after the screw moves forward, the resin is simply compressed in the nozzle and a flow into the die does not occur at then, so that a time lag between the screw movement and the output of pressure within the die takes place in general.
FIG. 1 is a schematic diagram of an injection mechanism of an injection molding machine to which an injection pressure control method is applied. In FIG. 1, a die 1, a cylinder 2, a screw 3, a hopper 4 for supplying pellets of resin into the cylinder, a front plate 5 constituting the injection mechanism, a rear plate 6, a plurality of guide bars 7 arranged between the front plate 5 and the rear plate 6 are arranged, and a pressure plate 8 is guided by the guide bars 7 and arranged such that the pressure plate 8 is movable forward and backward (the left and right directions in FIG. 1). The base portion of the screw 3 is pivotally attached to the pressure plate 8, and a pulley is attached to the base portion, and the screw 3 is rotationally driven by a screw rotation servo motor M1 through a drive pulley, a timing belt, and the like. A ball nut 10 is attached to the pressure plate 8 through a pressure sensor 9 (load cell), a ball screw 11 is meshed with the ball nut 10, and the ball screw 11 is rotationally driven by an injection servo motor M2 through a drive pulley, a timing belt, and a driven pulley.
In the injection step, the injection servo motor M2 is driven, the ball screw 11 is rotated, the ball nut 10 meshed with the ball screw 11 and the pressure plate 8 move forward (in the left direction in FIG. 1), and the screw 3 moves forward to inject melted resin in the cylinder 2 into the cavity of the die 1. At this time, although the injection pressure is detected by the pressure sensor (load cell) 9, the resin pressure detected by the pressure sensor (load cell) 9, i.e., the injection pressure, is that at the rear end portion of the screw 3, and is not resin pressure at the resin inlet port of the die 1. As a result, the pressure detected by the pressure sensor 9 is different from the resin pressure at the resin inlet port of the die 1, the pressure which serves as a reference of the resin flow analysis in the CAE.
A nozzle 12, the melted resin in the cylinder 2, the screw 3, and the pressure plate 8 are interposed between the point at which the resin pressure is detected by the pressure sensor and the resin inlet port of the die 1. For this reason, a pressure loss is generated between the point at which the resin pressure is detected by the pressure sensor and the resin inlet port, and a flow of the resin into the die delays because the nozzle end is sharply reduced in diameter so that the resin is compressed in the nozzle. When the pressure in the nozzle increases to some extent, the resin passes through the nozzle portion and is injected into the die. For these reasons, after the injection is started, a lag time between the detection of the pressure by the pressure sensor 9 and the output of the pressure in the die is generated.
For these reasons, the results of the CAE related to the pressure at the resin inlet port of the die cannot be directly used as molding conditions, compensation for the time lag discussed above and compensation for the pressure loss must be performed by any method.
It is an object of the present invention to make it possible to obtain an injection pressure curve of molding conditions by a simple method using resin flow analysis results obtained by the CAE.
In order to achieve the above object, there is provided an injection molding condition forming method including the step of obtaining a resin pressure curve at a resin inlet port of a die by a resin flow analysis for analyzing a flow of resin in the die; the step of obtaining an injection pressure curve in an air shot; and the step of obtaining an injection pressure curve serving as a molding condition based on the injection pressure curve in the air shot and the resin pressure curve obtained by the resin flow analysis.
According to another aspect of the present invention, there is provided an injection molding condition forming method in an injection molding machine wherein, in the step of obtaining an injection pressure curve serving as the molding condition, the injection pressure curve in the air shot is used as the injection pressure curve serving as the molding condition during a lag time between the start of injection by the molding machine and injection of resin from the nozzle end, and thereafter, the resin pressure curve at the resin inlet port of the die and the injection pressure curve in the air shot are added to each other, and the addition result is used as the injection pressure curve serving as the molding condition
There is provided an injection molding condition forming method in an injection molding machine further including the step of calculating a pressure loss curve in an area extending from the pressure sensor to the resin inlet port of the die by the resin flow analysis, and wherein, in the step of obtaining an injection pressure curve serving as the molding condition, the injection pressure curve in the air shot is used as the injection pressure curve serving as the molding condition during a lag time between the start of injection by the molding machine and injection of resin from the nozzle end, and thereafter, the resin pressure curve at the resin inlet port of the die and the pressure loss curve in the area extending from the pressure sensor to the resin inlet port of the die are added to each other, and the addition result is used as the injection pressure curve serving as the molding condition.
According to still another aspect of the present invention, there is provided an injection molding condition forming method in an inject molding machine including the step of obtaining a resin pressure curve of a cylinder-side end of a molding machine nozzle portion obtained by a resin flow analysis using a resin flow path in a die and the nozzle portion of the molding machine as objects to be analyzed; the step of obtaining an injection pressure curve in an air shot; and the step of obtaining an injection pressure curve serving as a molding condition based on the injection pressure curve in the air shot and the resin pressure curve obtained by the resin flow analysis.
According to still another aspect of the present invention, there is provided an injection molding condition forming method in an injection molding machine wherein, in the step of obtaining an injection pressure curve serving as the molding condition, the injection pressure curve in the air shot is used as the injection pressure curve serving as the molding condition during a lag time between the start of injection by the molding machine and injection of the resin from a nozzle end, and thereafter, the resin pressure curve obtained by the resin flow analysis is used as the injection pressure curve serving as the molding condition.
According to still another aspect of the present invention, there is provided an injection molding condition forming method wherein, in at least the resin flow analysis of the nozzle portion, an analysis in consideration of a pressure dependence of a resin viscosity is performed.
According to still another aspect of the present invention, there is provided a molding condition forming method in an injection molding machine wherein, in the step of obtaining an injection pressure curve in the air shot, the injection pressure curve is formed under a new condition based on known air shot injection pressure curves data stored in storage means in which known injection pressure curves data in air shots that are actually measured under various conditions are stored.
According to still another aspect of the present invention, there is provided a molding condition forming method in an injection molding machine wherein, in the step of obtaining an injection pressure curve m the air shot, an injection pressure curve in an air shot with respect to a resin temperature and an injection velocity of the molding conditions in the molding is formed by interpolating actually measured injection pressure curves data for air shots performed at s plurality of levels of resin temperatures and injection velocities for the same shape of the cylinder and that of the nozzle of the molding machine and the same resin to use.
According to still another aspect of the present invention, there is provided an injection molding machine including means for storing a resin pressure curve at a resin inlet port of a die calculated by a resin flow analysis for analyzing a flow of resin in the die; means for obtaining an injection pressure curve in an air shot; and means for obtaining an injection pressure curve serving as a molding condition based on the injection pressure curve in the air shot and the resin pressure curve obtained by the resin flow analysis.
According to still another aspect of the present invention, there is provided an injection molding machine wherein, in the means for obtaining an injection pressure curve serving as the molding condition, the injection pressure curve in the air shot is used as the injection pressure curve serving as the molding condition during a lag time between the start of injection by the molding machine and injection of resin from a nozzle end, and thereafter, the resin pressure curve at the resin inlet port of the die and the injection pressure curve in the air shot are added to each other, and the addition result is generated as the injection pressure curve serving as the molding condition.
According to still another aspect of the present invention, there is provided an injection molding machine further including the means for performing a resin flow analysis to a pressure loss curve in an area extending from a pressure sensor to the resin inlet port of a die, and wherein, in the means for obtaining an injection pressure curve serving as the molding condition, the injection pressure curve in the air shot is used as the injection pressure curve serving as the molding condition during a lag time between the start of set injection and injection of resin from a nozzle end, and thereafter, the resin pressure curve at the resin inlet port of the die and the pressure loss curve extending from the pressure sensor to the resin inlet port of the die are added to each other, and the addition result is generated as the injection pressure curve serving as the molding condition
According to still another aspect of the present invention, there is provided an injection molding machine including: means for storing a resin pressure curve of a cylinder-side end of a nozzle portion of molding machine obtained by a resin flow analysis using a resin flow path in a die and a nozzle portion of the molding machine as objects to be analyzed; means for obtaining an injection pressure curve in an air shot; and means for obtaining an injection pressure curve serving as a molding condition based on the injection pressure curve in the air shot and the resin pressure curve obtained by the resin flow analysis.
According to still another aspect of the present invention, there is provided an injection molding machine wherein, in the means for obtaining an injection pressure curve serving as the molding condition, the injection pressure curve in the air shot is used as the injection pressure curve serving as the molding condition during a lag time between the start of injection and injection of the resin from a nozzle end, and thereafter, an injection pressure curve is generated by using the resin pressure curve obtained by the resin flow analysis as the molding condition.
According to still another aspect of the present invention, there is provided an injection molding machine further including storage means for storing injection pressure curve data in an air shot and actually measured under various conditions, and wherein, in the means for obtaining an injection pressure curve in the air shot, an injection pressure curve under a new condition is formed based on known air shot injection pressure curves data stored in storage means.
According to still another aspect of the present invention, there is provided an injection molding machine further including storage means for storing actually measured injection pressure curves data in air shots performed at a plurality of levels of resin temperature and injection velocities for the same shape of the cylinder and that of the nozzle of the molding machine and the same resin, and wherein, in the means for obtaining an injection pressure curve in the air shot, the actually measured injection pressure curves data stored in the storage means are interpolated, so that an injection pressure curve in an air shot with respect to a resin temperature and an injection velocity of the molding conditions in the molding is formed.
According to still another aspect of the present invention, there is provided an injection molding condition forming apparatus comprising a resin flow analyzing device for obtaining a resin pressure curve at a resin inlet port of a die by a resin flow analysis for analyzing a flow of resin in the die and an injection molding machine for obtaining an injection pressure curve in an air shot, wherein the injection molding machine calculates an injection pressure curve serving as a molding condition based on the resin pressure curve given by the resin flow analyzing device and the injection pressure curve in the air shot.
According to still another aspect of the present invention, there is provided an injection molding condition forming apparatus comprising a resin flow analyzing device for obtaining a resin pressure curve of a cylinder-side end of a molding machine nozzle portion by a resin flow analysis using a resin flow path in a die and the nozzle portion of the molding machine as objects to be analyzed and an injection molding machine for obtaining an injection pressure curve in an air shot, wherein the injection molding machine calculates an injection pressure curve serving as a molding condition based on the resin pressure curve given by the resin flow analyzing device and the injection pressure curve in the air shot.
According to still another aspect of the present invention, there is provided a computer readable storage medium which stores a program for causing a computer of a control device for controlling an injection molding machine to execute: the step of obtaining a resin pressure curve at resin inlet port of a die by a resin flow analysis for analyzing a flow of resin in the die; the step of obtaining an injection pressure curve in an air shot; and the step of obtaining an injection pressure curve serving as a molding condition based on the resin pressure curve obtained by the resin flow analysis and the injection pressure curve in the air shot.
According to still another aspect of the present invention, there is provided a computer readable storage medium which stores a program for causing a computer of a control device for controlling an injection molding machine to execute: the step of obtaining an injection pressure curve in an air shot; and the step of obtaining an injection pressure curve serving as a molding condition based on the injection pressure curve in the air shot obtained in the above step and a resin pressure curve at a resin inlet port of a die obtained by a resin flow analysis for analyzing an input flow of resin in the die.
According to still another aspect of the present invention, there is provided a computer readable storage medium which stores a program for causing a computer of a control device for controlling an injection molding machine to execute: the step of obtaining a resin pressure curve of a cylinder-side end of a nozzle portion of a molding machine obtained by a resin flow analysis using a resin flow path in a die and the nozzle portion of the molding machine as objects to be analyzed; the step of obtaining an injection pressure curve in an air shot; and the step of obtaining an injection pressure curve serving as a molding condition based on the resin pressure curve obtained by the resin flow analysis and the injection pressure curve in the air shot.
According to still another aspect of the present invention, there is provided a computer readable storage medium which stores a program for causing a computer of a control device for controlling an injection molding machine to execute: the step of obtaining an injection pressure curve in an air shot; and the step of obtaining an injection pressure curve serving as a molding condition based on the injection pressure curve in the air shot obtained in the above step and a resin pressure curve at a cylinder-side end of the molding machine nozzle portion obtained by a resin flow analysis using an input resin flow path in a die and the nozzle portion of the molding machine as objects to be analyzed.